High-frequency transformer



May 8, 1945.

c. T. MCCOY 2,375,309

HIGH FREQUENCY TRANSFORMER Filed Jan. 29, 1943 Patented May 8, 1945 HIGH-FREQUENCY TRANSFORMER Claudius T. McCoy, Philadelphia, Pa., assignor to Philco Radio and Television Corporation, Philadelphia, Pa., a corporation of Delaware Applicationv January 29, 1943, Serial No. 473,989

8 Claims.

between the windings, and this requires that the windings be disposed very close to one another. In the past, it has been customary to secure a high degree of coupling by winding one coil directly upon the other, but this has not proven satisfactory in many applications since such practice is inherently one of low precision, and when employed in quantity production it requires a considerable amount of adjustment and resort to cut-and-try methods.

By the present invention, there is provided a transformer construction comprising a pair of coil forms or supports having precise dimensions and adapted to provide and maintain a predetermined high degree of coupling between the transformer windings.

The invention may be clearly understood from the following detailed description with reference to the accompanying drawing, in which Fig. l is a perspective view showing the parts of the transformer prior to assembly;

Fig. 2 is a cross-sectional view of the assembled transformer;

Fig. 3 'is an electrical diagram showing the transformer as a coupling agent between a pair of tubes;

Fig. 4 is an elevational view showing the transformer mounted in association with the tubes;

Fig. 5 is a diagrammatic plan view showing the preferred arrangement when a plurality of transformers are employed in association with a plurality of cascaded tubes; and

Fig. 6 is a sectional view of a modified form of the transformer.

Referring to Figs. 1 and 2, the transformer comprises an outer coil form or support I, a, coil or a winding 2 thereon, an inner coil form or support 3, and a coil or winding 4 on the latter support. The coil supports I and 3 may be formed of any suitable material. In the case of an air-core transformer, these parts may be formed of suitable insulating material, such as hard rubber or Bakelite, which has the necessary characteristics for precision manufacture of the said supports. Moreover, the coil supports may be manufactured by any method by which it is possible to attain precise dimensions. For example, known methods of molding and/or machining may be employed.

The coil supports are generally of cylindrical form and the outer support I is open at one end, as shown in Fig. 1, to receive the inner support 3. The opposite end of the outer coil support is substantially closed to provide an end wall surface 5 against which the inner coil support may abut. The relatively thick end wall 6 is provided with a central opening I which is threaded throughout at least a portion of its length, the purpose of which will be explained later. The coil-carrying portion 8 of support I- has exact inner and outer diameters so that the wall of said portion is of predetermined exact thickness. A pair of shoulders 9 and ID are provided on the support I at predetermined exact positions and these shoulders serve to define the length of the coil-carrying portion.

. The inner coil support has a cylindrical coilcarrying portion I l of predetermined exact diameter, and a pair of flanges I2 and 13 which define the length of portion II and which are of predetermined exact diameter such that they will fit snugly within the outer coil support, as shown in Fig. 2. These flanges serve to fix the position of the inner winding 4 in relation to the inner cylindrical surface l4 of the outer coil support. Moreover, the diameter of the flanges I2 and I3 is slightly greater than the outside diameter of the coil 4 so that the flanges prevent the coil or winding from rubbing against the surface l4 during assembly of the parts. The inner coil support also has end projection l5 and I6 of reduced diameter and of predetermined exact axial length, one of which abuts against the end wall surface 5, and fixes the axial position of the inner winding relative to the outer winding. In this manner, the upper edge of flange l2 (as viewed in Fig. 2) is precisely aligned with the shoulder 9. These elements determine or flx the position of the lowermost turn of each winding and, therefore, these end turns of the windings are positioned exactly adjacent to one another.

Preferably, the coil-carrying portions 8 and H of the coil supports are similar in length and are somewhat longer than is necessary for the axial length of the windings normally employed. By following this practice, the same coil forms may be employed without change in a large variety of systems having different, characteristics, the coils being only of sufficient axial length to give the desired inductance.

It will be seen that the exact positioning of the windings, which is obtained by the structure of the coil forms, causes the outer windin 2 to overlie the inner winding 4 and also causes the spacing between the windings to be exactly fixed. If the flanges I2 and I3 are extended beyond the outer surface of winding 4 only enough to protect the winding, the spacing between the windings is determined primarily by the thickness of the cylindrical wall 8. In practice, this wall thickness may be of the order of ,64. of an inch or less, depending upon the materials used and the stresses to which the parts will be subjected. It is evident, of course, that the spacing between the windings may be determined by the difference in diameters of the inner coil form 3 and flanges l2 and [3.

When the parts are assembled by inserting one part within the other, as shown in Fig. 2, the open end of the outer coil support may be sealed by means of a suitable sealing material l1. Ordinary sealing wax may be employed for this purpose. However, when the parts are constructed to fit very closely, as is preferred, a tight friction fit is obtained between them which is adequate to hold them in fixed relation.

The lead wires for the windings are preferably arranged as illustrated. Openings or passages l8 and I9 are provided in the outer coil support to accommodate the lead wires and 2| for the outer winding. The end projections 15 and I6 of the inner coil support are provided with transverse openings or passages 22 and 23 through which the lead wires 24 and 25 extend. The flanges I2 and i3 are recessed at 26 and 2! and the ends of the winding 4 extend through these recesses and are connected to the respective lead wires. An openin or passage 28 is provided in the outer coil support to accommodate the lead wire 24.

Figs. 3 and 4 illustrate the transformer employed as a coupling means between two tubes 29 and 30 which are preferably pentodes. Although the windings of the transformer may be tuned by physical capacities, at the high frequencies for which the transformer is primarily adapted, the windings may be conveniently tuned by the output and input capacities of the tubes 29 and 30, as shown in Fig. 3 by the broken line representations 3| and 32. If it is desired that the frequency characteristic of the transformer be relatively fiat over its pass band, one or both of the windings may be provided with a suitable shunt resistor, as shown at 33 and 34 in Fig. 3.

As illustrated in Fig. 4, the transformer may be suspended from the panel 35 (preferably metal) on which the tubes are mounted. To this end, a screw 36 extends through the panel 35 and engages the threaded opening I of the outer coil support I. The transformer is mounted in such relation to the tubes as to permit the use of very short leads between the transformer and the connecting lugs of the tube sockets 31 and 38. Preferably, the high potential leads 2! and 25, which are connected respectively to the grid of tube 30 and the anode of tube 29, are taken from the end of the transformer furthest removed from the socket-carrying panel 35, so as to minimize the distributed capacity between the said leads and the panel. The low potential leads are normally by-passed to the metal panel 35 and hence there is no problem of distributed capacity with respect to such leads.

Where a substantial number of tubes are cascaded and a plurality of transformers are em ployed to couple the successive tubes, the layout of Fig. 5 is preferably employed since it provides a very desirable economy of space. In this figure, the tubes are represented at 39 while the transformers are represented at 40. In conventional single-ended tubes, 1. e. tubes in which both the control grid and plate connections are made through the base, it is customary for the plate and grid pins to be disposed on opposite sides of the tube base, as shown by the symbols P and G in Fig. 5. In the layout scheme of Fig. 5, the high potential lead connected to the plate of a given tube is widely spaced from the high potential lead connected to the grid of the said tube, and hence the danger of undesired feedback from the output circuit of the tube is held to a minimum.

In Fig. 6 there is illustrated a modified form of the device in which the coil supports la and 3a are both held in place by a single fastening means in the form of a bolt II which is preferably of non-magnetic material. To this end the inner coil support is hollow and has an apertured end wall 42, the aperture of which is aligned with a passage 43 in the outer coil support. Otherwise the device is substantially the same as that previously described. For simplicity the details of the coil connections are omitted from the illustration which only concerns the mounting of the coil forms.

In one physical embodiment of the invent-ion, a transformer was constructed to provide a band width of 18 megacycles, with a center or resonant frequency of 16 megacycles. Measurements showed the gain of the transformer to be substantially constant over the range 7 to 25 megacycles. The physical specifications of the transformer were as follows. The outside diameter (winding portion) of the inner coil support was 0.460 inch. The inside diameter of the outer .coil support was 0.475 inch. The outside diameter (winding portion) of the outer support was 0.525 inch. The forms were wound with No. 35 enameled wire having a diameter of 0.006 inch, there being 38 turns on each of the forms. In practice the primary may be either the outer or inner winding as desired. In some cases minor differences in characteristics between the windings may make it desirable to determine by test the particular selection of primary and secondary windings. In the embodiment described a shunt resistor of 1200 ohms was connected across the primary winding, while a shunt resistor of 500 ohms was connected across the secondary winding.

While the transformer has been illustrated and described as an air-core transformer, it is entirely within the scope of the invention to provide an iron-core structure which will be found particularly desirable where the device is employed over lower frequency ranges than that above described.

It will be understood, of course, that the invention is not limited to the specific embodiments illustrated, but is capable of various modifications within the scope of the appended claims.

I claim:

1. A high frequency transformer, comprising a hollow outer coil support open at one end and having a wall with a threaded opening at its opposite end, said support having an inner cylindrical wall surface of predetermined diameter. a coil or winding on the outer surface of said support, an inner coil support having spaced circularflanges of predetermined diameter such that aerasce they flt snugly within the cylindrical wall surface of the outer support, said inner support being slidably insertable within the outer support in abutment with the end wall surface thereof, a coil or winding on the outer surface of said inner support between said flanges, said lastnamed winding being slightly spaced from the cylindrical wall surface of said outer support when the parts are assembled as aforementioned, and means for sealing the open end of said outer support to retain said inner support therein, whereby the assembled device may be suspended by a screw engaging the said threaded opening.

2. A high frequency transformer, comprising a hollow outer coil support, a coil or winding thereon, an inner coil support disposed within said outer support, a coil or winding on said inner support, mutually cooperative-means on said supports for maintaining said windings in exact predetermined relation to one another, and a common securing element extending through both of said supports to maintain them in position and to support the assembled transformer.

, 3. A high frequency transformer, comprising a hollow outer coil support, a coil or winding thereon, an inner coil support disposed within said outer support, a coil or winding on said in ner support, mutually cooperative means on said supports for maintaining said windings in exact predetermined relation to one another, and a'se curing bolt extending through both of said sup-'- ports to maintain them in position and to support the assembled transformer.

4. A high frequency transformer, comprising a hollow outer coil support open at one end and thereof, said inner support being housed within said outer support and having its inner end abutting said wall whereby it is precisely locatedlengthwise of said outer support, said inner support having-a pair of external circumferential flanges spaced apart lengthwise and proportioned diametrically to fit snugly within said bore, the

peripheral area between said last-mentioned flanges being of reduced diameter, and a second winding carried by said peripheral area having one of itsend turns located immediately adja-' having a wall with an opening at its opposite end, said support having an inner cylindrical wall surface of predetermined diameter, a coil or winding on the outer surface of said support, an inner coil support having spaced circular flanges of predetermined diameter such that they flt snugly within the cylindrical wall surface of the outer support, said inner support being slidably insertable within the outer support in abutment with the end wall surface thereof, a coil or wind ing on the outer surface of said inner support be tween said flanges, said-last-named winding being slightly spaced from the cylindrical wall sur- -face of said outer support when the parts are assembled as aforementioned, said inner support having an opening aligned with said first-named opening, and a securing bolt extending through the aligned openings.

5. A high frequency transformer comprising a unitary cylindrical outer coil support having a 3 cent a predetermined one of said last-mentioned flanges whereby said second winding is definitely "located lengthwise with respect to said first wind- 6. A high frequency transformer having precise close coupling between its windings and adapted for precision and quantity production, comprising a unitary hollow cylindrical support having a tubular coil-carrying portion of predetermined exact wall thickness, and having an exterior annular shoulder at one end of the coil-carrying surface, said support being open at one end and having a wallat its opposite end, a coil wound about said portion and positioned lengthwise of said support by having one of its end turns located immediately adjacent said shoulder, a

unitary cylindrical support disposed within said hollow support in abutment with said end wall and adapted to fit snugly therein, said inner support having a cylindrical coil-carrying surface of predetermined exact diameter so as to position a coil thereon closely adjacent to the coilcarrying portion of the outer support, said inner S p rt also having a shoulder precisely located to position a coil axially in exact relationship with the coil on the outer support, and a coil wound about the coil-carrying surface of said inner support and having one of its and turns lo- 0' cated immediately adjacent said last-mentioned circumferential exterior coil-receiving surfacei situated intermediately of its ends and deflned lengthwise by a pair of spaced external flanges, which are integral parts of said support, a coil carried by said support and wound therearound on said surface and positioned lengthwise of said support by having one of its end turns located immediately adjacent one of said flanges, said outer support having a lengthwise extending bore which is open at one end and limited at the other endbyawalldesignedtofunctionasastona unitary cylindrical inner coil support proporl tioned'to flt telescopically within said bore and l tobeinsertedinsaidbore'thrcugh the open endshoulder.

l. A high frequency transformer, comprising a hollow cylindrical coil support having one end open, a coil wound upon said support, a solid cylindrical coil support disposed within said hollow support and having end projections with transverse openings or passages therethrough, a. coil wound upon said solid support, andlead wires for said last-mentioned coil extending to the interior of said hollow support and through said passages.

8. A high frequency transformer, comprising a hollow cylindrical coil support having one end open and a wall at its opposite end, said support also having a passage extending from the interior space adjacent said wall to the exterior of the support, a coil wound upon said support, a solid cylindrical coil support disposed within said hollow support and having end projections with.

transverse openings or passages therethrough, one of said end projections abutting said wall, a coil wound upon said solid support, and lead wires for said last-mentioned coil extending to the interior of said hollow support and through said last-mentioned passages, one of said lead wires extending through said first-mentioned usa e. p CLAUDIUB 1. MCCOY. 

